The present invention generally relates to the field of low resistivity ceramics. In particular, it relates to a new zirconia-based material in which the electrical conductivity can be controlled in a range to provide for its use as an electrostatic dissipative or "ESD" material.
Currently the ESD market is served by organic i.e. plastic materials. Organic based materials such as electro-conductive resin composite materials lend themselves to inexpensive molding processes and can be tailored to meet specific resistance requirements. U.S. Pat. No. 5,409,968 Controlled Conductivity Antistatic Articles illustrates such materials for use as an ESD material. This group of materials suffers significant shortfalls in their mechanical properties, heat resistance, and chemical resistance thereby limiting their usefulness.
There are numerous ceramic materials variously referred to as electro-conductive ceramics. Some are conductive in the bulk state, others upon doping or admixture with other materials. Each has limitations making it unsuitable for ESD applications e.g., a narrow range of specific resistance that cannot be adjusted for ESD applications. Others are much too conductive for use as an ESD materials. Many suffer from poor mechanical properties and do not make useful structural materials.
Electro-conductive composite ceramics typically consist of a mix of a electroconductive material with a ceramic material with a relatively high electrical resisitivity. These phases are variously interdispersed to yield some combination of the properties of each. The electro-conductive material can be a metal or a conductive ceramic. U.S. Pat. Nos. 4,110,260, 2,528,121 and 5,830,819 describe such materials. Such materials can be difficult to prepare requiring expensive processing such as hot-pressing to produce. Additionally some of these suffer from poor mechanical properties.
Many materials which might be contemplated for producing electro-conductive composite ceramics are not compatible at the high temperatures required in typical ceramic processing. The various components will chemically interact with the result being that the beneficial properties of the separate materials are degraded upon reaction.
This invention provides an electro-conductive composite ceramic with both the electrical and mechanical properties to render it particularly useful for applications such as ESD materials.